import java.util.Scanner;

public class d491 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String input, output;
		String[] spInput;
		int tempA, tempB;
		int a, b;
		int sum;
		
		while(sc.hasNext()) {
			input = sc.nextLine();
			spInput = input.split(" ");
			tempA = Integer.parseInt(spInput[0]);
			tempB = Integer.parseInt(spInput[1]);
			
			if(tempA < tempB) {
				a = tempA;
				b = tempB;
			} else {
				a = tempB;
				b = tempA;
			}
			
			if((a % 2) != 0)
				{ a++; }
			
			sum = 0;
			for(int i = a; i <= b; i += 2)
				{ sum += i; }
			
			output = Integer.toString(sum);
			
			System.out.println(output);
		} // next
	} // main
}